1. Field of the Invention
The present invention relates to a method for forming a DLC (diamond like carbon) film on a male spline section of a spline shaft by utilizing a hot cathode PIG plasma CVD device, and also to a hot cathode PIG plasma CVD device.
2. Description of the Related Art
In propeller shafts used in vehicles for example, two shafts are mated to each other by splines to permit axial sliding movement. The spline sections require slide capability and wear resistance. The forming of a DLC (diamond like carbon) film on these spline sections to meet such requirements is known in the related art (See Japanese Patent Application Publication No. 2011-122663 (JP 2011-122663 A)).
Methods for forming the DLC film are known to include CVD (chemical vapor deposition) methods, PVD (physical vapor deposition) methods, ion vapor deposition methods, etc. The CVD methods also include a hot cathode PIG (Penning Ionization Gauge) plasma CVD method (see Japanese Patent Application Publication No. 2006-169589 (JP2006-169589 A)) that uses a hot cathode PIG plasma source.
Generally, plural spline shafts are placed inside a device and a DLC film is formed simultaneously on the male spline sections of the plural spline shafts. Irregularities in film thickness of the DLC film formed on the respective male spline sections are preferably reduced in order to lower individual variations in performance among the plural male spline sections.